U.S. patent application number 14/778668 was filed with the patent office on 2016-05-05 for polymer sliding material with dry-run capability and slide ring seal with dry-run capability.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Florian Grimm, Armin Kayser, Ursula Kayser.
Application Number | 20160122682 14/778668 |
Document ID | / |
Family ID | 47901895 |
Filed Date | 2016-05-05 |
United States Patent
Application |
20160122682 |
Kind Code |
A1 |
Kayser; Armin ; et
al. |
May 5, 2016 |
POLYMER SLIDING MATERIAL WITH DRY-RUN CAPABILITY AND SLIDE RING
SEAL WITH DRY-RUN CAPABILITY
Abstract
The invention relates to a polymer sliding material, capable of
running dry and comprising a polymer matrix material and fillers,
wherein the fillers comprise reinforcing particles, hard material
particles and lubricant particles. The invention furthermore
relates to a mechanical seal, comprising a rotating sealing ring
and a stationary counter ring, wherein the sealing ring and/or the
counter ring encompass the polymer sliding material, which is
capable of running dry. Furthermore, the invention relates to the
use of such polymer materials, which are capable of running dry,
for dry-running applications, especially as a material for
displacement elements in wet-running and dry-running pumps.
Inventors: |
Kayser; Armin; (Groenenbach,
DE) ; Kayser; Ursula; (Buchenberg, DE) ;
Grimm; Florian; (Kempten, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
47901895 |
Appl. No.: |
14/778668 |
Filed: |
March 21, 2014 |
PCT Filed: |
March 21, 2014 |
PCT NO: |
PCT/EP2014/055707 |
371 Date: |
December 16, 2015 |
Current U.S.
Class: |
277/405 ;
277/407; 508/126 |
Current CPC
Class: |
C10M 107/46 20130101;
C10M 169/04 20130101; F16J 15/3496 20130101; C10M 125/02 20130101;
C10M 107/38 20130101; C10M 125/26 20130101; C10M 107/32 20130101;
C08K 3/013 20180101 |
International
Class: |
C10M 169/04 20060101
C10M169/04; C10M 107/38 20060101 C10M107/38; F16J 15/34 20060101
F16J015/34; C10M 125/02 20060101 C10M125/02; C10M 125/26 20060101
C10M125/26; C10M 107/32 20060101 C10M107/32; C10M 107/46 20060101
C10M107/46 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2013 |
EP |
13160642.8 |
Claims
1. A polymer sliding material, comprising a polymer matrix material
and fillers, wherein the fillers comprise reinforcing particles,
hard material particles and lubricants.
2. The polymer sliding material of claim 1, wherein the polymer
matrix material is selected from the group consisting of polyether
ether ketones (PEEK), polyaryl ether ketones (PAEK), polyphenylene
sulfides (PPS), polyether sulfones (PES, PESU), polyaryl sulfones
(PSU, PPSU), polyether imides (PEI), polyamides (PA), liquid
crystalline polymers (LCP) and combinations thereof.
3. The polymer sliding material of claim 1, wherein the reinforcing
particles comprise fibrous particles.
4. The polymer sliding material of claim 3, wherein the fibrous
particles comprise carbon fibers and/or aramide fibers.
5. The polymer sliding material of claim 1, wherein the content of
reinforcing particles is 1-20% by weight.
6. The polymer sliding material of claim 1, wherein the hard
material particles are selected from the group consisting of
silicon carbide, boron carbide, aluminum oxide, silicon dioxide,
zirconium oxide, silicon nitride and diamond particles and
combinations thereof.
7. (canceled)
8. The polymer sliding material of claim 1, wherein the hard
material particles comprise submicron particles.
9. The polymer sliding material of claim 1, wherein the content of
hard material particles is 1-30% by weight.
10. The polymer sliding material of claim 1, wherein the total
content of reinforcing particles and hard material particles is
2-50% by weight, based on the polymer sliding material.
11. The polymer sliding material of claim 1, wherein the lubricants
are selected from the group consisting of graphite,
polytetrafluoroethylene (PTFE), boron nitride and molybdenum
disulfide (MoS.sub.2) particles and combinations thereof.
12. (canceled)
13. The polymer sliding material of claim 1, wherein the total
content of lubricants is 1-40% by weight, based on the polymer
sliding material.
14. The polymer sliding material of claim 1, wherein the total
content of reinforcing particles, hard material particles and
lubricants is 3-70% by weight, based on the polymer sliding
material.
15. The polymer sliding material of claim 1, wherein the proportion
of hard material particles in the total amount of reinforcing
particles and hard material particles is 20-90% by weight.
16. The polymer sliding material of claim 1, wherein the proportion
of hard material particles in the total amount of hard material
particles and lubricants is 10-70% by weight.
17. The polymer sliding material of claim 1, wherein the proportion
of reinforcing particles in the total amount of reinforcing
particles and lubricants is 10-70% by weight.
18. The polymer sliding material of claim 1, wherein the modulus of
elasticity of the polymer sliding material is at least 7 GPa.
19. A mechanical seal, comprising a rotating sealing ring and a
stationary counter ring, wherein the sealing ring and/or the
counter ring encompass a polymer sliding material of at least claim
1.
20. The mechanical seal of claim 19, wherein the sealing ring is
constructed from a polymer sliding material of claim 1, and the
counter ring is constructed from steel.
21. The mechanical seal of claim 19, wherein the sealing ring is
constructed from a polymer sliding material of claim 1, and the
counter ring is constructed from a sintered ceramic.
22-23. (canceled)
24. A use of the polymer sliding material of claim 1 as a material
for a displacement element in wet-running and dry-running pumps.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polymer sliding material,
which is capable of running dry, to a mechanical seal and a sealing
ring of a polymer sliding material, which is capable of running dry
as well as to the use of such materials for dry-running
applications, especially as displacement elements in wet-running
and dry-running pumps.
BACKGROUND OF THE INVENTION
[0002] Medium-lubricated mechanical seals are used, for example, as
drive shaft seals in pump drives, where they seal liquid pressure
from the surroundings and from the driving mechanism. Because of
their simple construction and their performance, pumps with
mechanical seals are widely used for conveying and circulating
liquids.
[0003] For this type of pump, about 50% of the damage is caused by
mechanical seals and more than half of these cases are attributed
to the fact that the mechanical seals have run dry. Dry running may
result from defective handling, especially if the supply of liquid
is interrupted.
[0004] Special constructions of mechanical seals can also run dry
permanently and, in so doing, seal the agitator shafts, for
example, at the bushing to the pressure vessels. Until now,
agitator seals have been made from the mechanical seal pairing of
graphite and silicon carbide. However, the performance of these
materials is limited. For many applications, especially the
resulting graphite abrasion is not acceptable.
[0005] For mechanical seals, which run dry permanently or are
lubricated by a medium, mechanical friction losses are dissipated
as heat input into the liquid lubricating medium and into the
bearing seats. In the absence of liquid lubrication under
dry-running conditions, frictional losses, and thus the input of
heat, are clearly increased. In addition, heat is not dissipated by
the liquid. As a result, in conventional seal pairings such as
SiC/SiC or Al.sub.3/AlO.sub.3, temperatures of more than
200.degree. C. develop within a few minutes and directly cause
thermal damage to the static secondary seals. The secondary seals
usually are constructed as O-rings from elastomeric materials. This
type of seal damage is responsible for about 50% of all pump damage
in modern circulating pumps.
[0006] Displacement pumps, such as vacuum vane pumps, when used as
brake boosters, are also not lubricated with a liquid in the
operating state. In this procedure, the displacement elements
(slide valves) which build up the pressure rub against the pump
housing. This leads to high tribological heat in the frictional
contact and to a high input of heat into the housing and the
driving mechanism. With this type of pump as well, heat damage is
the main cause of failure after long dry-running times.
[0007] In other displacement pumps, such as gear pumps, the
displacement elements (gear wheels) are braced between pressure
plates. The frictional contact between the pressure plates and the
gear wheels, both of which usually are made from steel, leads to
high frictional and performance losses. When running dry
temporarily, a thermal overload may easily occur.
PRIOR ART
[0008] In present-day types of pumps, with a medium-lubricated
shaft-mechanical seals, usually a mechanical seal pairing,
consisting of a rotating sealing ring of graphite and a stationary
counter ring of sintered ceramic, is used. With these pairings,
long service lives of up to 10 years of constant operation can be
achieved at coefficients of friction of about 0.05 with liquid
lubrication and of about 0.15 with brief dry-running times.
[0009] Polytetrafluoroethylene (PTFE) can also be used as an
alternative to graphite as the material for the rotating sealing
ring. However, because of its very low pressure and very low wear
resistance, the pairing of PTFE with ceramic is suitable only for
seals, which must withstand only a very small load, and it has not
been used widely.
[0010] For medium-lubricated shaft mechanical seals which can
withstand a significantly higher load, mechanical seal pairings,
from the combination of ceramic against ceramic and preferably from
sintered silicon carbide (SSiC) against SSiC, are used. With these
pairings, coefficients of friction of about 0.05 can be attained
with liquid lubrication; however, the dry-running coefficients of
friction of about 0.8 are very high. These sealing ring pairings
can therefore be used in dry-running operations for only a few
minutes. By using variations of the silicon carbide material, for
example, silicon carbide with graphite additives, slightly longer
dry-running times of about 10 minutes are possible. However, these
materials can also not be used for permanent dry-running
operations.
[0011] At the present time, the material pairing of graphite and
ceramic is therefore used for liquid-lubricated mechanical seals
for uses, in which the sealing must be suitable for temporary
dry-running operations.
[0012] Until now, no suitable pairs of materials have been
available to the designer for permanent dry-running of mechanical
seals. Because only brief dry-running times are possible, the
pairing of graphite and ceramic as a mechanical seal cannot be used
for a permanent dry-running application. In addition, this pairing
is also disadvantageous because of strong noise development and
because abraded graphite is discharged from the mechanical seal.
Especially for agitator seals, which must be capable of running dry
permanently, both effects are undesirable during use.
[0013] A structural solution for a mechanical seal, which is
capable of running dry permanently, is the construction of the
mechanical seal as a so-called gas seal, in which ceramic is paired
with ceramic, the dry friction being lowered greatly by building up
a gas film between the friction partners. However, very high RPMs,
generally of above 10,000, are required for this purpose. Moreover,
this solution is structurally very expensive and, until now, has
been used only for larger installations such as gas compressors for
overland pipelines.
[0014] Until now, polymer-based materials have not yet found wide
use in media-lubricated mechanical seals or displacement pumps,
although, especially for reasons of simplifying the process and the
system and of lowering the costs associated therewith, the
proportion of polymer materials in pump components has increased
with each new generation of pumps. The material-related
disadvantages of polymer-based materials are the poor dissipation
of heat because of low thermal conductivity of less than 1.0 W/m*K,
low dimensional stability under pressure and wear resistance, which
has not been adequate until now. The high output of frictional heat
which results during the operation of mechanical seals is
dissipated very poorly by polymer materials. Moreover, the polymer
materials already fail at comparatively low temperatures.
Circulation pumps frequently are operated in pressurized water
systems at about 140.degree. C. Under these conditions, many
conventional polymers fail due to hydrolysis and/or loss of
mechanical strength.
[0015] WO 2012/169604 A1 describes a sealing ring which is produced
from a resin composition containing polyphthalamide. In addition,
the resin composition may contain fillers, such as carbon fibers,
glass fibers, silicon carbide fibers, graphite, MoS.sub.2,
Al.sub.2O.sub.3, MgO, boron nitride and PTFE powder. However, the
ceramic fillers, in the form of particles of fibers, lead to high
wear at the tribological partners, and the resin compositions are
not capable of running dry. The matrix material cannot be processed
thermoplastically.
[0016] WO 2010/054241 A2 describes a method for producing a
thermoplastic sealing ring, especially for seals of a very large
diameter. For this purpose, an extruded strand is shaped into a
ring and joined to the front face. The thermoplastic polymers may
contain PTFE or carbon black as fillers.
[0017] In displacement pumps, such as vane pumps, sintered
graphites have established themselves as the standard material for
the slide elements for wet-running and for dry-running briefly.
Some patent applications have also already proposed the use of
polymer-based materials. However, the use of polymer-based
materials, due to their so far unsatisfactory dry-running
capability, has been limited to liquid-lubricated pumps.
[0018] DE 10 2008 019 440 A1 proposes the use of polymer materials
for slide valves in dry-running vacuum pumps. The polymer materials
used have no advantage over graphite in dry-running operations and
have only limited wear resistance.
[0019] DE 20 2009 000 690 U1 describes a rotary displacement pump
with bearings and displacement elements made from polymer materials
such as Teflon or PEEK.
[0020] DE 20 2007 012 565 U1 describes a displacement pump with a
rotor of a PEEK material.
[0021] The EP 1 424 495 A2 describes a positive displacement pump
with a pump rotor and/or a rotor blade of polymer materials such as
PEEK, PPS and PES. The materials listed have only limited
dry-running capabilities, that is, they can run dry for only a
short time and also only under moderate loads.
OBJECT OF THE INVENTION
[0022] The invention therefore addresses the object of avoiding the
disadvantages of the prior art and making a polymer sliding
material available, as well as a mechanical seal made therefrom,
which exhibits low losses due to friction and is wear resistant
even over long running times under wet-running conditions and which
is also capable of running dry permanently. Furthermore, the
invention addresses the object of making available a polymer-based
sliding material for displacement elements in dry-running pumps,
the material making it possible to extend the dry-running time.
SUMMARY OF THE INVENTION
[0023] The above-named object is achieved by the polymer sliding
material of claim 1, the mechanical seal of claim 19 and the use of
the polymer sliding material of claim 24. Preferred or especially
appropriate embodiments of the polymer sliding material and of the
mechanical seal are given in the dependent claims 2-18 and
20-23.
[0024] The subject matter of the invention accordingly is a polymer
sliding material, comprising a polymer matrix material and fillers,
the fillers comprising reinforcing particles, hard material
particles and lubricants.
[0025] A further subject matter of the invention is a mechanical
seal, comprising a rotating sealing ring and a stationary counter
ring, the rotating sealing ring and/or the counter ring surrounding
an polymer sliding material according to the invention.
[0026] A further subject matter of the invention is the use of such
materials for dry-running applications, especially as a material
for displacement elements in pumps running wet and dry.
[0027] The polymer sliding material according to the invention is
wear resistant and mechanically stable and, unlike graphite, is
capable of running dry permanently. The wear resistance is better
than that of graphite.
[0028] The polymer sliding material according to the invention
makes very low losses due to friction possible in wet-running and
dry-running. It is suitable for permanent dry-running operations as
a rotating sealing ring and/or as a stationary counter ring in
mechanical seals and as displacement elements and wet-running and
dry-running pumps, for example, as slide valves in vane pumps.
[0029] The mechanical seal according to the invention produces very
low frictional losses and is distinguished by being able to run dry
permanently.
[0030] The mechanical seal according to the invention can be
produced cost-effectively and is distinguished by operating with
little noise when running dry.
[0031] The operation of dry-running pumps with little noise is made
possible by the use of the polymer sliding material according to
the invention as displacement elements.
[0032] Preferably, the polymer sliding material according to the
invention has a low specific density of 1.4-1.6 g/cm.sup.3. This is
a further advantage over graphite (density 2.2 g/cm.sup.3) and, in
rotary displacement pumps, additionally lowers the performance
losses due to the reduced normal force acting on the friction
partner.
[0033] The polymer sliding material according to the invention can
be produced by injection molding, which makes the production of
components with many design possibilities simple and
cost-effective.
[0034] Sintered graphite materials which have previously been used
as standard materials in pump applications can therefore be
replaced by the polymer sliding materials according to the
invention. As a result, polymer materials can be used for the first
time in mechanical seals in pumps, which are operating under a
slight to a moderate load of up to about 16 bar.
[0035] The dry-running coefficients of friction of the mechanical
seal according to the invention are lower than those of comparable
mechanical seals with polymer materials which were produced with
the addition of reinforcing fibers and dry lubricants but without
using hard material particles, especially submicron ceramic
particles.
[0036] This improvement in properties was not expected since
ceramic materials generally have very high dry coefficients of
friction and are not capable of running dry. The dry coefficients
of frictions of ceramic/steel and ceramic/ceramic pairings are
>0.5. On the other hand, sintered graphites, when paired with
steel and ceramic, have dry coefficients of frictions of 0.15-0.2.
The dry coefficients of friction, achievable with the mechanical
seals according to the invention, are below 0.1 and thus below the
values achievable with the standard pairings of graphite and
ceramic or graphite and steel. This improvement in properties is
also surprising for a person skilled in the art.
[0037] A further advantage of the mechanical seal according to the
invention is that the temperature increases only slightly in
dry-running operations, which is necessary especially for
protecting secondary polymer seals, such as O-rings.
[0038] When running dry, even at very high loads, such as
rotational speeds of 3000 RPM and surface pressures of 0.6 MPa, the
investigated rotating sealing rings of the polymer sliding material
according to the invention exhibit a very flat surface which is
almost free of traces of wear. Even after a longer period of use of
one hour, the sliding surface is flat and shows only the slightest
effects of positive mechanical engagement. Therefore, a very low
coefficient of friction is maintained even under continuous
operating conditions without liquid lubrication.
[0039] Under wet-running conditions, the coefficients of friction
of the mechanical seal according to the invention with the polymer
material according to the invention as the rotating sealing ring
and Al.sub.2O.sub.3 ceramic as the counter ring of 0.015 are in the
middle of the values measured and, accordingly, are less by a
factor of 3 than the coefficients of frictions of conventional
mechanical seals made from graphite and ceramic.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Materials, with a high chemical resistance in the media,
used in household and motor vehicle circulating pumps, such as
water, oil, brake fluid and glycol, are suitable as polymer matrix
materials for the polymer sliding material according to the
invention. Furthermore, the polymer matrix materials should be
suitable for continuous operation at the maximum use temperatures.
The maximum use temperatures are 140.degree. C. for water and
220.degree. C. for oil. The glass transition temperature of the
polymer matrix material should be higher than these temperatures.
For manufacturing reasons, the polymer matrix material preferably
should be thermoplastically processable. Furthermore, the polymer
matrix materials should have a good pressure resistance and a high
modulus of elasticity for absorbing the mechanical forces with
little deformation.
[0041] These requirements are fulfilled particularly by the
high-temperature plastics, which can be processed
thermoplastically, are used preferably as polymer matrix materials
and comprise materials of the following classes: polyether ether
ketones (PEEK), polyaryl ether ketones (PAEK), polyphenylene
sulfides (PPS), polyether sulfones (PES, PESU), polyaryl sulfones
(PSU, PPSU), polyether imides (PEI), polyamides (PA) and liquid
crystalline polymers (LCP). However, other polymer matrix materials
may also be used, such as the following, which cannot be processed
thermoplastically: polyimide (PI), polybenzimidazole (PBI) and
polytetrafluoroethylene (PTFE). Combinations of these classes of
material are also possible.
[0042] The polymer sliding material according to the invention
contains fillers, which can also be referred to as tribo additives.
Reinforcing particles, lubricants and hard material particles are
used as fillers.
[0043] The function of the reinforcing particles is to reinforce
the polymer material mechanically. In particular, fibrous particles
such as carbon and/or aramide fibers, are suitable as reinforcing
particles. The addition of reinforcing particles increases the
modulus of elasticity of the polymer materials. As the modulus of
elasticity increases, the elastic deformation at a given pressure
decreases, whereby the pressure absorbing capability of the pump
components produced therefrom, such as the rotating sealing ring,
and the load carrying capability of the mechanical seal increase.
Because they support the sliding properties and reduce the
abrasiveness at the counter ring of the mechanical seal, the use of
carbon fibers as mechanical reinforcing particles for the polymer
sliding material according to the invention is particularly
preferred.
[0044] The content and the particle size or fiber length of the
reinforcing particles is selected in such a way that the stiffness
and strength values, which are optimal for the respective design,
result. Preferably, the content of reinforcing particles is 1-20%
by weight and particularly 5-20% by weight, based on the polymer
sliding material.
[0045] Preferably, the length of the fibers, preferably used as
reinforcing particles, such as carbon fibers, is less than 200
.mu.m, since longer fibers are not stable during compounding and
injection molding.
[0046] As hard material particles for the polymer sliding material
according to the invention, silicon carbide, boron carbide,
aluminum oxide, silicon dioxide, zirconium dioxide, silicon nitride
and diamond particles may be used. Combinations of these hard
material particles are also possible. Preferably, silicon carbide,
boron carbide, aluminum oxide and silicon dioxide particles or
combinations of these particles are used.
[0047] Preferably, silicon carbide particles are used as hard
material particles. Silicon carbide fillers have a hardness of
>9.5 Moh and are thus harder than all naturally occurring
abrasive materials (with the exception of diamonds). In addition,
in almost all liquid pump media, silicon carbide has very good
corrosion resistance which exceeds by far that of known polymer
matrix materials.
[0048] A further advantage of the version with silicon carbide
fillers is the very high thermal conductivity of silicon carbide of
more than 120 W/mK, whereby the resulting frictional heat can be
dissipated effectively even in the composite material.
[0049] Since coarse-grained ceramic fillers are highly abrasive
when processed and in tribological contact with the counter ring,
very fine grains with an average particle size (d.sub.50) of not
more than 1 .mu.m are preferably used as hard material particles.
It is particularly preferred if the average particle size
(d.sub.50) of the hard material particles is less than 1 .mu.m
(submicron particles) and even more preferred if it does not exceed
0.8 .mu.m.
[0050] The hard material particles preferably have a low aspect
ratio (the ratio of length to diameter) of 2 or lower; this has an
advantageous effect on reducing abrasion.
[0051] The content of hard materials can be selected over a wide
range up to the limit of the theoretical packing density of the
particles. Preferably, the content of hard material particles is
1-30% by weight; good mechanical properties of the polymer material
are obtained with these contents. It is particularly preferred if
5-20% by weight hard material particles are added, in each case
based on the polymer sliding material.
[0052] The total content of reinforcing particles and hard material
particles is preferably 2-50% by weight and particularly 10-30% by
weight, based on the polymer sliding material.
[0053] The mixing ratio of reinforcing particles to hard material
particles is selected according to the hardness, stiffness and
strength desired for the respective application.
[0054] As lubricants, graphite, polytetrafluoroethylene (PTFE),
boron nitride and molybdenum disulfide (MoS.sub.2), for example,
are suitable. Silicone oils also come into consideration.
Lubricants are preferably used in the form of lubricating
particles.
[0055] The average particle size (d.sub.50) of the lubricating
particles is preferably 1-50 .mu.m.
[0056] The use of combinations of graphite and PTFE particles as
lubricating particles is particularly preferred.
[0057] The total content of lubricants is preferably 1-40% by
weight and particularly 10-30% by weight, based on the polymer
sliding material.
[0058] For processing reasons, the total content of reinforcing
particles, hard material particles and lubricants should not exceed
70% by weight. The total content of reinforcing particles, hard
material particles and lubricants is preferably between 3 and 70%
by weight and particularly between 30 and 50% by weight, based on
the polymer sliding material. The total content of polymer matrix
material is preferably 30-97% by weight and particularly 50-70% by
weight, based on the polymer sliding material.
[0059] In relation to the total amount of hard material particles
and reinforcing particles, the hard material particles are
preferably contained in an amount of 20-90% by weight and
particularly of 40-80% by weight.
[0060] In relation to the total amount of hard material particles
and lubricants, the hard material particles are preferably
contained in an amount of 10-70% by weight and particularly of
25-60% by weight.
[0061] In relation to the total amount of reinforcing particles and
lubricants, the reinforcing particles are preferably contained in
an amount of 10-70% by weight and particularly of 25-45% by
weight.
[0062] In a preferred embodiment, a combination of carbon fibers,
SiC submicron particles and lubricant particles are used as fillers
for the polymer sliding material according to the invention. Here
also, it is advantageous to use the preferred combination of
graphite and PTFE particles as lubricant particles.
[0063] The modulus of elasticity, i.e., the stiffness of the
polymer sliding material according to the invention is at least 7
GPa.
[0064] The rotating sealing ring and/or the rotating counter ring
of the mechanical seal according to the invention encompasses the
polymer sliding material according to the invention. In a preferred
embodiment, the rotating sealing ring and/or the stationary counter
ring of the mechanical seal according to the invention is
constructed from the polymer sliding material according to the
invention.
[0065] The sliding partner of the rotating sealing ring or counter
ring of the mechanical seal according to the invention,
encompassing the polymer sliding material according to the
invention, that is, the stationary counter ring or also the
rotating sealing ring, may be constructed from conventional
mechanical seal materials, such as ceramic, graphite, hard metal,
metal or bronze.
[0066] In a further possible embodiment, both the rotating sealing
ring and the stationary counter ring are made from a polymer
material; preferably, both rings are made from the polymer sliding
material according to the invention. By these means, the total
costs of the mechanical seal can be reduced even further.
[0067] Preferably, the rotating sealing ring of the mechanical seal
according to the invention is constructed from the polymer sliding
material according to the invention.
[0068] In a preferred embodiment of the mechanical seal according
to the invention, the rotating sealing ring is made from the
polymer sliding material according to the invention, and the
counter ring is made from steel. This embodiment is particularly
suitable for oil and hydraulic applications.
[0069] In a further preferred embodiment of the mechanical seal
according to the invention, the sealing ring is made from the
polymer sliding material according to the invention and the counter
ring from a tight and finely grained sintered ceramic, such as
aluminum oxide. The construction from a sintered silicon carbide
(SSiC) is particularly advantageous. A suitable silicon carbide
material is attainable under the name of EKasic.RTM. F from ESK
Ceramics GmbH & Co. KG and has a thermal conductivity of
>120 W/mK.
[0070] The sliding surface of the rotating sealing ring and/or of
the stationary counter ring preferably should have a very high
surface quality, i.e., low roughness values. It was possible to
show that the coefficient of friction and wear could be
significantly reduced by decreasing the roughness values of the
sealing ring and/or of the counter ring. It is particularly
preferred if both the sealing ring and the counter ring have a
polished sliding surface.
[0071] The sliding surface of the counter ring should preferably be
constructed with little deviation from flatness.
[0072] The polymer sliding material according to the invention may
be used continuously under dry-running conditions.
[0073] Aside from its use in a mechanical seal, the polymer sliding
material according to the invention can also be used as a
displacement element in wet-running and dry-running pumps. Examples
of displacement elements are slide valves in displacement pumps
such as vacuum vane pumps and pressure plates in gear pumps.
Furthermore, the polymer sliding material according to the
invention may also be used as a component in radial and axial
bearings.
[0074] Displacement elements of the the polymer sliding material
according to the invention and mechanical seals according to the
invention can be used in hot water circulating pumps, drinking
water pumps, cold water circulating pumps for internal combustion
engines and electric drives, compressor pumps for condensation
cooling cycles, vacuum pumps for brake boosters, displacement pumps
for brake fluids (ESP and ABS systems), cooling water circulating
pumps for cooling control cabinets, hydraulic units and laser
devices.
[0075] Aside from dry-running applications, the displacement
elements of the polymer sliding material according to the invention
can also be used for applications in corrosive media such as
alkaline solutions and acids, solvents, oils, low-viscosity fats
and brake fluids.
[0076] Furthermore, the mechanical seal according to the invention
is also suitable for seals in electric motors, especially in small
motors, as long as permanent lubrication with oils, fats or other
lubricants is ensured.
[0077] The polymer sliding material according to the invention is
preferably converted by a thermoplastic injection molding process
into components such as sealing rings and counter rings of the
mechanical seal according to the invention and into displacement
elements. Components with demanding complexity and functional
integration requirements can also be produced on an industrial
scale by the thermoplastic injection molding process. Customary
methods of the art, such as twin screw extrusion, are used for
mixing and compounding the polymer sliding materials.
[0078] To improve the dispersing properties, the hard material
particles, before they are mixed and compounded, may be
agglomerated, for example, by spray-drying. The average size of the
agglomerates is preferably 70-150 .mu.m here. The agglomerates
easily disintegrate during the compounding with twin screw
extrusion under standard settings and permit an efficient extrusion
process even at high contents of hard material particles of up to
30% by weight. Processing of not agglomerated hard material
particles is not preferred for particle sizes in the submicron
range.
[0079] Other known prior art methods for producing polymer matrix
materials may also be used for preparing the polymer sliding
material according to the invention.
EXAMPLES AND COMPARATIVE EXAMPLES
Example 1
[0080] A filled polymer material is prepared by means of
thermoplastic twin screw extrusion. The composition for the
compounding by means of twin screw extrusion comprises 60% by
weight PEEK (Victrex.RTM. PEEK 150), 10% by weight graphite, 10% by
weight PTFE, 10% by weight carbon fibers and 10% by weight silicon
carbide powder.
[0081] The silicon carbide powder has a purity of >96% and an
average particle size (d.sub.50) of 150 nm. In order to improve the
dispersing properties, the silicon carbide powder is agglomerated
by spray-drying from an aqueous suspension. The average size of the
spray-dried agglomerate is 100 .mu.m.
[0082] The agglomerates easily disintegrate during the compounding
with twin screw extrusion at standard settings and make an
efficient extrusion process possible.
Example 2
[0083] A filled polymer material is prepared by means of
thermoplastic twin screw extrusion. The composition for the
compounding in the twin screw extruder comprises 55% by weight PPS
(Fortron 0203 from Ticona), 10% by weight graphite, 10% by weight
PTFE, 10% by weight carbon fibers and 15% by weight silicon carbide
powder. The agglomerated powder, used in Example 1, is employed as
silicon carbide powder.
Example 3
[0084] A filled polymer material is prepared by means of
thermoplastic twin screw extrusion. The composition for the
compounding in the twin screw extruder comprises 60% by weight PESU
(Polyether sulfone; Ultrason E 1010, BASF), 10% by weight graphite,
10% by weight PTFE, 10% by weight carbon fibers and 10% by weight
silicon carbide powder. The powder, used in Example 1, is employed
as silicon carbide powder.
Example 4
[0085] The dry-running test is carried out in a test rig of the
ring-on-ring type. For this purpose, rings of the material of
Example 1 are produced for the stator by processing extruded rods
mechanically. The rings have an external diameter D.sub.a of 30 mm,
and internal diameter D.sub.i of 20 mm and a height h of 16 mm. The
sliding surface of the rings is polished finely, and the rings are
subsequently inserted in the stator sample holder of the dry-run
test rig. A ring of 1.4713 stainless steel with a finely polished
surface is inserted in the sample holder for the rotor. The sliding
surface of the stator is pressed pneumatically with a contacting
pressure of 0.2 NiPa against the sliding surface of the rotor.
After the motor is started, the rotor rotates at 1000 RPM, which
corresponds to an average sliding speed of 1.3 m/s. The stator is
mounted so that it can rotate and is held by a wire which leads to
a load cell, so that the transmitted frictional force can be
measured. A thermocouple which measures the temperature, is also
fastened to the stator. The coefficient of friction is calculated
from the measurement signal of the load cell and, together with the
temperature, is recorded as a function of time.
[0086] The coefficient of friction .mu. is calculated from:
.mu.=(F.sub.LMD*r.sub.LMD)/(p.sub.Flache*A.sub.Reib*r.sub.Reib)
[0087] in which
[0088] F.sub.LMD [N] is the frictional force, measured by the load
cell
[0089] r.sub.LMD [mm] is the radius, at which the frictional force
is measured
[0090] p.sub.Flache [N/mm.sup.2 is the surface pressure of the
rings
[0091] A.sub.Reib [mm.sup.2] is the engaging surface area
[0092] r.sub.Reib [mm] is the average radius of the friction
surface.
[0093] The average coefficient of friction over the whole of the
running time, determined from the measurements obtained, as well as
the temperature measured at the stator after one hour of the
experiment, serve as evaluating parameters for the ability to run
dry.
[0094] Table 1 shows the obtained measurements.
[0095] The higher the coefficient of friction, the greater the
frictional energy, in the form of heat, and the faster the rise in
temperature. The temperature depends not only on the heat of
friction which has been introduced, but also on the thermal
properties of the friction partners (heat capacity, thermal
conductivity, heat flow into the sample and, over the sample
holder, into the whole of the measurement apparatus). If the
coefficient of friction is low, the temperature increases only
slowly and then levels off at a plateau value, which is indicated
in Table 1 in the "Comments" column by the statement "Plateau
value". This behavior is observed for all of the examples according
to the invention. At high coefficients of friction, the temperature
increases continuously until, at a temperature of >150.degree.
C., the test rig switches off.
[0096] The suitability of the examples of Table 1 for dry-running
is given in Table 2, separately for the emergency mode of operation
and for continuous use.
[0097] Materials which cope with a brief failure of the lubricating
medium without overheating are rated as capable of running dry
without overheating. In this connection, a time of up to 30 minutes
is considered as brief. Materials which lead to overheating or
which fail after a few minutes are not capable of running dry in an
emergency mode of operation.
[0098] Materials which can run for a longer time without a
lubricating medium without overheating are classified as being
capable of running dry for continuous use. A time of one hour or
more is considered as a longer time. A further essential criterion
for the capability to run dry permanently is the adjustment of a
constant temperature level (plateau) below a temperature which is
critical for the system components (for example, for the
experiments conducted here, the maximum temperature of 150.degree.
C. permissible for the test rig). This is the case when the heat of
friction, introduced into the system during the dry running, is so
slight, that it can be absorbed by the system or dissipated once
again without a further rise in temperature. By such means, it is
ensured that the temperature remains low permanently.
Example 5
[0099] Example 4 was repeated; however, the stator was produced
from the material of Example 2.
[0100] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
Examples 6-8
[0101] Example 4 was repeated; however, the contacting pressure and
the sliding speed were varied as shown in Table 1.
[0102] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
[0103] Even after very high loads, such as rotational speeds of
1000 RPM and at surface pressure of 0.6 MPa, the friction specimens
of the materials according to the invention, examined after the
dry-running test of Examples 4-8 had been carried out, showed a
very flat surface which was almost free of traces of wear.
Reference Example 1
[0104] The dry-running test of Example 5 was repeated; however, the
stator ring for the dry-running test was prepared from a material
corresponding to Example 1, however, without the addition of
submicron hard material particles of silicon carbide. As fillers
for the PEEK material, 10% by weight graphite, 10% by weight PTFE
and 10% by weight carbon fibers were used (70% by weight PEEK).
[0105] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
[0106] The experiment was terminated after 4.5 minutes since the
temperature at the stator was already 70.degree. C. and a further
temperature increase as steep as this would have led to the melting
of the stator.
Reference Example 2
[0107] The dry-running test of Example 5 was repeated; however, the
stator ring for the dry-running test was prepared from a material
corresponding to Example 2, however, without the addition of
submicron hard material particles of silicon carbide. As fillers
for the PPS material, 10% by weight graphite, 10% by weight PTFE
and 10% by weight carbon fibers were used (70% by weight PPS).
[0108] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
[0109] The experiment was terminated after 2.5 minutes since the
temperature at the stator was already 70.degree. C. and a further
temperature increase as steep as this would have led to the melting
of the stator.
Comparative Example 1
[0110] The dry-running test of Example 5 was repeated; however,
with the exception that the stator ring for the dry-running test
was produced from carbon graphite (EK3205, SGL Carbon) which had
been impregnated with antimony. The contacting pressure was 0.2 MPa
and the sliding speed was 1.3 m/s (as in Example 5, see Table
1).
[0111] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
[0112] After an experimental period of 60 minutes, the temperature
at the stator was 120.degree. C. and still rising. Accordingly, the
mechanical seal pairing is not capable of running dry under
continuous use conditions.
[0113] The mechanical seal pairing tested can be used for the
emergency mode of operation; however the removal by abrasion of
this pairing is significantly higher than that of Examples 4 and 5
according to the invention (see Table 1, last column).
Comparative Example 2
[0114] The dry-running test of Example 8 was repeated; however,
with the exception that the stator ring for the dry-running test
was produced from carbon graphite (EK3205, SGL Carbon) which had
been impregnated with antimony. The contacting pressure was 0.6 MPa
and the sliding velocity was 3.9 m/s (as in Example 9, see Table
1).
[0115] The measurements obtained are given in Table 1 and the
evaluation of the dry-running ability is given in Table 2.
[0116] The experiment was terminated after 24 minutes, since the
stator temperature was already 150.degree. C. and the dry-running
test rig was not designed for higher temperatures.
TABLE-US-00001 TABLE 1 Dry-Running Test of the Ring-on-Ring Type
Average Contacting coefficient of Temperature pressure p friction
for the (stator) Abrasion at [MPa]/Sliding- whole of the after 60
min the stator Example No. Stator speed [m/s] running time
[.degree. C.] Comments [.mu.m/h] Example 4 Example 1 0.2/1.3 0.074
52 Plateau value 1.91 Example 5 Example 2 0.2/1.3 0.098 50 Plateau
value 2.48 Example 6 Example 1 0.4/1.3 0.035 48 Plateau value n.d.
Example 7 Example 1 0.6/1.3 0.038 60 Plateau value n.d. Example 8
Example 1 0.2/3.9 0.037 47 Plateau value n.d. Reference PEEK with C
0.2/1.3 0.34 >70 max. running 14.1 Example 1 fibers/graphite/
time 4.5 min, PTFE since T > 70.degree. C. was reached Reference
PPS with C 0.2/1.3 0.59 >70 max. running n.d. Example 2
fibers/graphite/ time 2.5 min, PTFE since T > 70.degree. C. was
reached Comparative Carbon graphite 0.2/1.3 0.19 120 T increases
13.6 Example 1 even more Comparative Carbon graphite 0.2/3.9 0.13
>150 max. running n.d. Example 2 time 24 min, since T >
150.degree. C. was reached n.d. = Not determined D.sub.a = 30 mm,
D.sub.i = 20 mm Dry running against steel rotor Temperature
measurement at the stator v = 1.3 m/s (1000 RPM) or 3.9 m/s (3000
RPM) p = 0.2 MPa or 0.4 MPa or 0.6 Mpa
TABLE-US-00002 TABLE 2 Dry-Running Dry-Running Capability
Capability Example No. Stator Emergency Mode Continues Use Example
4 Example 1 yes yes Example 5 Example 2 yes yes Example 6 Example 1
yes yes Example 7 Example 1 yes yes Example 8 Example 1 yes yes
Reference PEEK with C no no Example 1 fibers/graphite/ PTFE
Reference PPS with C- no no Example 2 fibers/graphite/ PTFE
Comparative Carbon graphite yes no Example 1 Comparative Carbon
graphite no no Example 2
* * * * *